1. Field of the Invention
This invention relates to a nitride semiconductor epitaxial wafer and a nitride semiconductor device.
2. Description of the Related Art
A nitride semiconductor including indium (In), gallium (Ga), aluminum (Al), nitrogen (N) and the like has a high saturation electron speed and a high breakdown voltage, thus it is put to practical use as a material for an electronic device or the like capable of realizing high efficiency and high output in a high frequency region. In addition, it is also expected as a key material ensuring for high performance of a power device achieving a high efficiency of an inverter that is key parts and components of an electric vehicle (EV), a hybrid electric vehicle (HEV) and the like.
A nitride semiconductor device such as a nitride semiconductor high frequency electronic device and a nitride semiconductor power device generally includes an epitaxial layer comprised of a nitride semiconductor including indium (In), gallium (Ga), aluminum (Al), nitrogen (N) and the like. In order to form a nitride semiconductor device having high performance, it is required that the nitride semiconductor epitaxial layer has a good crystallinity.
As an index of the crystallinity of the nitride semiconductor epitaxial layer of the nitride semiconductor device, a method is known, the method being configured such that a full width half maximum of X-ray rocking curve in a predetermined plane is used (see e.g., JP-B-3836697). JP-B-3836697 determines an upper limit value of the full width half maximum of X-ray diffraction spectrum as a condition of high crystallinity.